The present invention relates to a printer having a power transmission change-over or switching mechanism, and more particularly, to the change-over mechanism for selectively transmitting driving power from a power source to a purging mechanism at a proper timing.
In an image recording apparatus such as an ink jet printer and a facsimile machine, ink ejection type image formation is known in which ink droplet is ejected from a nozzle of a print head onto an image recording medium such as a paper sheet to form an inked image. In such a type of the image recording apparatus, bubbles may be generated in the print head, or ink may be adhered onto the surface of the nozzle of the print head, which cause insufficient ink ejection. In order to avoid this drawback and to recover sufficient ink ejecting fashion, a maintenance device such as a purging mechanism is provided in the apparatus.
According to the purging mechanism a suction cap is mounted on the print head, and negative pressure is generated by a pump so as to suck interior ink and bubbles in the print head. As a drive source for driving the pump and other components in the purging mechanism, a line feed motor is commonly used which serves as a drive source for feeding the printing sheet in a sheet feeding direction, that is for driving a platen. With this arrangement, parts and components can be reduced, and production cost can be lowered.
In such an image recording apparatus in which the drive source is commonly used for driving the purging mechanism as well as the sheet feeding mechanism, a power transmission change-over mechanism is provided so as to selectively transmit the driving power from the power source to the purging mechanism. More specifically, there are provided a power transmission gear to which driving power from the drive source is transmitted, a drive gear or negative pressure gear for driving the purging mechanism, and a drive gear or feed gear for driving the sheet feeding mechanism. The power transmission gear is selectively engageable with the negative pressure gear or the feed gear, so that at least one of or both the negative pressure gear and the feed gear are rotatable. The power transmission gear is moved to a position to meshingly engage the negative pressure gear so as to drive the purging mechanism, when a carriage mounting thereon the print head is moved to a capping position where the print head is covered with a protection cap provided in the image recording apparatus.
However, in the above described conventional power transmission change-over mechanism, if the carriage is moved to another position from the capping position, the power transmission gear is disengaged from the negative pressure gear even if the purging mechanism is still operated. Therefore, if the electrical power supply is shut off while the nozzle recovery operation is performed when the carriage is positioned at the capping position, and if an operator manually moves the carriage to a position other than the capping position during turning OFF state of the electrical power, the power transmission gear is disengaged from the negative pressure gear even if the nozzle recovery operation has not been completed. Consequently, it would be difficult to restore the previous position, i.e., it would be difficult to again engage the power transmission gear with the negative pressure gear. This may cause breakdown or damage of the image recording apparatus.
Further, if the above described conventional changeover mechanism is provided in a color printer in which a plurality of print heads are provided for ejecting inks of different colors, and if a single purging mechanism is provided for successively performing nozzle recovery operation with respect to each print head, the carriage must be successively moved so that each one of the print heads is moved to a position in confrontation with the single purging mechanism. Due to this movement of the carriage, the power transmission gear may be disengaged from the negative pressure gear. Accordingly, it would be difficult to smoothly and equally perform nozzle recovery operation for the all nozzles of the print heads.